[vector] PHP multiline errors are collected line by line when detectMultilineErrors is enabled.

Description of problem:

When deploy vector as the collector and enable detectMultilineErrors, the PHP errors are still collected line by line:

Version-Release number of selected component (if applicable):

Logging 5.7.0

How reproducible:

Always

Steps to Reproduce:

1. Create a pod to generate multiline errors 
2. Enable detectMultilineErrors in CLF
3. Deploy logging using vector as the collector

Actual results:

PHP errors are collected line by line

Expected results:

PHP errors should be treated as single message. 

Additional info: